Long ago, Halli Sveinsson’s ancestors fought monsters in the valley and drove them up into the hills. Halli wants to be a hero too, but when he rebels against his peaceful, boring life, he unleashes a series of terrible events. With the help of a girl called Aud, who is just as brave and curious as he is, Halli begins to piece together the secrets of the valley – but what they uncover threatens to destroy them . . .